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Separation of marsh tits paruspalustris and willow tits parusmontanusGraham W. Scott aa School of Environmental Sciences , University College ,Scarborough, Filey Road, Scarborough, North Yorkshire, YO113AZ, UKPublished online: 11 Apr 2011.

To cite this article: Graham W. Scott (1999) Separation of marsh tits parus palustris and willowtits parus montanus , Ringing & Migration, 19:4, 323-326, DOI: 10.1080/03078698.1999.9674201

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Ringing & Migration (1999) 19, 323-326

Separation of Marsh Tits Parus palustris and Willow TitsParus montanus

GRAHAM W. SCOTT School of Environmental Sciences, University College,Scarborough, Filey Road, Scarborough, North Yorkshire YO11 3AZ, UK

Various published criteria for the separation of Marsh and Willow Tit in the handwere tested on a sample of birds caught for ringing. Only tail 'shape' and the differencein length between T6 and T3 proved reliable. It is suggested that this criterion shouldbe given the most weight, with others used as supporting features, when separatingbirds in the hand.

The identification of Marsh Tit Parus palustrisand Willow Tit Pants montanus is considered

by many to be problematical (Cramp & Perrins1993). The problem becomes even more confusedin continental situations where numerous racesof both species may be encountered (Cramp &Perrins 1993). In fact such is the nature of thepossible confusion that UK races warrant aspecial mention in the Ringer's Manual (Spencer1995) which provides a list of plumage charactersringers might use to separate them (see Table 1).Whilst a list of this type is undeniably useful whena ringer is able to compare birds of the twospecies, it is perhaps more common to trap singlebirds. In such a situation, with nothing forcomparison, these characters may be less useful.Wing length differences are also considereduseful (Spencer 1995) with a wing in the range58-67mm suggesting a Marsh Tit and one in therange 55-63mm suggesting a Willow Tit (althoughconsiderable overlap must therefore exist).

Perrins (1979) suggests that the difference inlength between the 'inner' and 'outer' tail feathersis greater in the Willow Tit (5-6mm) than in theMarsh Tit (2-4mm). In a recent issue of theRingers' Bulletin Chris and Richard de Feu (1996)add a further character to the list. They suggestthat the arrangement of tail feathers in the twospecies differs such that in the Marsh Tit T6 isconsiderably shorter than any of the other tailfeathers which are themselves similar in lengthto one another, the effect being that there is aclear 'gap' between T6 and T5 whilst T5 coversthe remainder of the tail. In the Willow Tit atleast three feathers are visible and clear 'gaps'between T5-T6, T4-T5 and T3-T4 exist.

At a winter feeding station in Dalby Forest,North Yorkshire, I am fortunate in that Ifrequently catch birds of both species (readilyidentified by their species specific calls). This hasprovided me with an opportunity to investigatethe various separation criteria. During the period

Table 1. Characters used to separate Marsh Tit and Willow Tit in the hand. Adapted from Spencer (1995)

Colour of crownSecondary fringesColour of flanks

Bib

Cap

(CC)(SF)(CF)

(Bb)

(Cp)

Marsh Tit

glossy blackas mantleas rest of underparts

clearer cut and lessextensiveextending less fardown nape

Willow Tit

very dark matt chocolatepaler than mantlericher buff than rest ofunderpartsless clear cut and moreextensiveextending further downnape

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324 Graham W. Scott

Figure 1. Distribution of Character scores (see text] inMarsh and Willow Tits. Solid bars indicate Marsh Tits,open bars indicate Willow Tits

January 1997 to January 19981 made a total of 36captures of 23 individuals of which 14 birds (20captures) were known to be Marsh Tits and 9birds (16 captures) were known to be WillowTits.

In order to compare the five key characterslisted in Table 1,1 allocated for each bird examineda score of 1 if it showed the Willow Tit characterstate and a score of 0 if it showed the Marsh Titcharacter state. Thus a Willow Tit should score 5overall and a Marsh Tit should score 0. The actualdistributions of scores recorded from the 36captures are presented in Fig 1 (as no informationabout a bird's history was available at the timeof capture inclusion of retrapped birds does notpose a problem in terms of data independence).In fact no birds scored 0 and only ten birds scored5. The birds known to be Marsh Tits scored 1,2or 3 and those known to be Willow Tits scored2,3,4 and 5. The reasons for these ambiguousscores can be seen in Table 2. From the table it is

Table 2. Reliability of characters. For each of the 5characters (CC, FC, Bb, CF, Cp) the number of times abirds was awarded the correct (0 for Marsh Tit and 2 forWillow Tit) and incorrect (2 for Marsh Tit and 0 forWillow Tit) character score. For abbreviations see Table 1

Species

Marsh Tit

Willow Tit

Character

0*202*

CC

13027

FC

12109

Bb

12127

CF

11209

Cp

01309

clear that only the colour of the crown (CC) wasunambiguous for Marsh Tit whilst the colour ofthe flanks (CF) and extent of the cap (Cp) wereunambiguous for Willow Tit. All of the othercharacters involved some ambiguity.

A significant proportion of the Willow Tits hadMarsh Tit-like bibs and caps (colour). Almost halfof the Marsh Tits had Willow Tit-like buff flanksand paler secondary fringes, and all of themwere deemed to have a cap "extending furtherdown nape" (Spencer 1995). Of course, onaverage the caps of Willow Tits do appear longerthan those of Marsh Tits but when making thedecision for a single bird with nothing forcomparison this feature appears too error-proneto be useful. From personal observations duringthe latter stages of this study the caps of the twospecies do differ, but in shape and 'edge' colourrather than in length. After smoothing with afinger the cap of a Marsh Tit narrows markedlyat the back of the head and remains narrow as itextends onto the mantle. In contrast, that of theWillow Tit does not narrow behind the head, andremains wider as it extends onto the mantle. Inmany cases I felt that this resulted in the cap of aMarsh Tit appearing to be more pointed overallthan that of a Willow Tit (though I could see thatboth did smooth to a point). However, thisobservation does not agree with the experienceof some other ringers working on otherpopulations of birds and collections of skins(Hounsome, pers. comm.). Their observationbeing that the Willow Tit has the more attenuatedcap. This highlights the need for caution whengeneralising subjective descriptions from personto person and from one area to another (andperhaps especially when generalising from UKto continental populations given the polytypicnature of both species).

Another apparent difference between the capsof the species in my study area was that thedemarcation between the cap and mantle is clear-cut in the Marsh Tit, but in the Willow Tit the cap'blends' into the mantle forming a rufous 'halo'effect (Fig 2).

Although the wing lengths (maximum chord)(Svensson 1992) of the two species were foundto differ significantly (Marsh Tit (n = 14) mean ±s.d. = 63.1 ± 1.56; Willow Tit (n = 9) mean + s.d. =59.9 ±2.1; t-test P < 0.001), there was considerableoverlap in the ranges (Marsh Tit 58-64; WillowTit 62 - 65). From these data it would not have

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Marsh Tit Willow Tit

Figure 2. The shape of the cap in the Marsh Tit and theWillow Tit. a = cap extension, b = mantle, c = rufous halo(see text)

Table 3 . Marsh Tit and Willow Tit tail shape.Measurements refer to mean differences in length betweenpairs of tail feathers, n = sample size, s.d. = standarddeviation

T6-T5T5-T4T4-T3T6-T3

Marsh

mean(mm)

2.50.50.13.2

Tit

s.d.

0.870.540.210.98

n

14141414

Willow

mean(nun)

3.11.20.75.0

Tit

s.d

0.460.610.470.82

n

9999

Separation of Marsh and Willozv Tits 325

been possible to separate the species on the basisof the wing lengths given by Spencer (1995).

To compare the tail feather patterns of thetwo species the differences in length between T6and T5, T5 and T4, and T4 and T3 were measuredto the nearest 0.1mm using dial reading callipers(these data are summarised in Table 3). TheMarsh Tits were found to have a gap between T6and T5, but little or no gap between either T5and T4 or T4 and T3. The Willow Tits were foundto have more evenly spaced feathers giving theunderside of the tail a gradually stepped effect(Fig 3). Thus the tail of the Marsh Tit is squarerthan that of the Willow Tit. The difference inlength between T6 and T3 in the two species issignificantly different (t-test t = 4.8; df = 21; P <0.001). Bearing in mind that the data are basedon small samples, it would appear that birds witha less than 4mm difference between T6 and T3are Marsh Tits and those with more than a 4mmdifference in length are Willow Tits. As Fig 4indicates, some overlap is apparent.

In summary, the two species could not beseparated on the basis of wing length in thispopulation. Similarly the majority of the plumagecharacters listed by Spencer (1995) appearinsufficient as separators, perhaps because of thesubjectivity involved in their allocation to singlebirds in the hand. Cap demarcation appears frominitial observations to be useful (though I admitthat it is no less subjective). In practice I suggestthat all of these plumage characters be consideredwhen obtaining an overall opinion of a bird.

T6

T6

T

T5T4

3

1n 1

0.5 "*2.5

T5

3.1

T4T3

(171.2

Marsh Tit

Willow Tit

Figure 3. Tail shape and tail feather length differences in the Marsh Tit and the Willow Tit. The figures cited refer tothe average differences (mm) recorded from the study population. The two sets of 'feathers' are drawn to the same scalefrom the tip of T6 for direct comparison. It should be noted that because Tl and T2 have not been included, and thefull lengths of the feathers are not shown, the figure gives the incorrect impression that the tail of the Marsh Tit isshorter than that of the Willow Tit, on average the reverse is in fact true (Hounsome pers. comm.).

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326 Graham W. Scoff

6

5

Freq

uttn

cy

2

1

0 II1 2 3 4 5 6

T6 - TJ diff.r.no

Figure 4. Distribution of T6 - T3 length differences (mm)in Marsh and Willow Tits. Solid bars indicate Marsh Tits,open bars indicate Willow Tits

More rigorous, and therefore more useful, werethe measurements involved in the comparisonof the lengths of T6 and T3, and the du Feu tailshape criterion. I suggest that these charactersshould be given most weight when identifyingan individual.

To conclude I would suggest that separationcriteria such as these can only be considereduseful if they can be generalised from this sampleto the wider population. Anyone regularlyhandling both Willow and Marsh Tits, even inmodest numbers, should therefore assess theirutility and share their findings with fellow ringers.

ACKNOWLEDGEMENTS

I would like to acknowledge the assistance ofthe members of the East Yorkshire RingingGroup, especially Peter Dunn who firstsuggested that I consider cap extension shape. Iwould like to thank the Forestry Commissionfor permission to ring in Dalby Forest. Chris duFeu and Mike Hounsome provided usefulcomments on an earlier draft of this manuscript.

REFERENCES

Cramp, S & Perrins, C.M., (eds) (1993) The Birds ofthe Western Palearctic. Vol VII. Oxford UniversityPress. Oxford.

du Feu C., & du Feu, R., (1996) Separating Marshand Willow Tits. Ringer's Bulletin, November 1996.

Perrins, C.M. (1979) British Tits. Collins. NewNaturalist. London.

Spencer, R. (1995) The Ringer's Manual. 3rd edition.The British Trust for Ornithology.

Svensson, L. (1992) Identification Guide to EuropeanPasserines. 4th edition. Svensson, Stockholm.

(MS received 25 June 1997; MS accepted 19 August 1998)

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